摘要:

Electric breakdown in GaNp‐njunctions was investigated. GaNp+‐p‐n+structures were grown on 6H–SiC substrates by metalorganic chemical vapor deposition. Mg and Si were used as dopants. Mesa structures were fabricated by reactive ion etching. Capacitance–voltage measurements showed that thep‐njunctions were linearly graded. The impurity gradient in thep‐njunctions ranged from 2×1022to 2×1023cm−4. Reverse current–voltage characteristics of thep‐njunctions were studied in the temperature range from 200 to 600 K. The diodes exhibited abrupt breakdown at a reverse voltage of 40–150 V. The breakdown had a microplasmic nature. The strength of the electric breakdown field in thep‐njunctions depended on the impurity gradient and was measured to be from 1.5 to 3 MV/cm. It was found that the breakdown voltage increases with temperature. The temperature coefficient of the breakdown voltage was ∼2×10−2V/K. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116469

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

High quality metastable pseudomorphic Si1−xGexepilayers were grown by ultrahigh vacuum chemical vapor deposition using Si2H6and GeH4. These epilayers were implanted with 40 keV B11+and 100 keV BF+2ions at a dose of 1×1015ions/cm2and then annealed by rapid thermal annealing (RTA) processes at temperatures of 600, 650, 700, and 750 °C for 30 s duration. Double‐crystal x‐ray diffractometry was used to evaluate the level of the implant‐induced damage and the damage removing efficiency of both ion implanted samples at different RTA conditions. The results show that the RTA process is more effective at removing damage from B11+implanted samples than from those implanted with BF+2. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116470

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ohmic contacts with low resistance are fabricated onn‐type GaN films using Ti/Ag bilayer metallization. The GaN films are grown by low pressure metalorganic chemical vapor deposition (LP‐MOCVD) with Si as the dopant. Ohmic characteristics are studied for films with carrier concentration range from 1.5×1017to 1.7×1019cm−3. The lowest value for the specific contact resistivity of 6.5×10−5&OHgr; cm2is obtained without annealing. The barrier height of Ti on GaN is calculated to be 0.067 eV. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116471

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Growth of Si and SiGe layers using molecular beam epitaxy was carried out with the substrate at a floating, positive or negative bias, in order to investigate effects of ion bombardment on the crystalline quality of grown materials. Although ion energies (100–1500 eV) and ion/atom flux ratios (∼0.005) used in the experiments were quite low, significant lattice distortion along the growth direction (&Dgr;a⊥/asup to ∼300 ppm) was observed by high resolution x‐ray diffraction from the Si layers grown at 420 °C. At the same time, a broadband transition was observed in photoluminescence measurements from both Si and SiGe layers. Based on results of the annihilation behavior during postgrowth treatments using thermal annealing and hydrogenation, we attribute these effects to the ion bombardment induced formation and injection of different types of pointlike defects and defect clusters, which degrade the optical and electrical properties of grown layers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116472

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on the fabrication and characterization of broadband Bragg filters in microfabricated AlGaAs waveguides. Electron‐beam lithography and chemically assisted ion‐beam etching were used to fabricate first‐order gratings with 250 nm period. Bragg filters with rejection bandwidth ∼15 nm and centered at ∼1.6 &mgr;m are demonstrated. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116473

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We useinsitureflection high‐energy electron diffraction to investigate the growth kinetics of cubic (001)‐GaN/GaAs grown by plasma‐assisted molecular beam epitaxy. We find that the GaN surface exhibits three surface reconstructions having (1×1), (2×2), andc(2×2) symmetries, which correspond to Ga adatom coverages of 0, 0.5, and 1, respectively. We demonstrate that the transient behavior of the half‐order streak intensity is a sensitive probe of the surface stoichiometry during growth. Particularly, these measurements enable us to directly determine the effective N flux incorporated into the crystal. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116474

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Injection of point defects into Si was examined by deep level transient spectroscopy. Preimplanted samples containing di‐vacancies and O‐vacancy pairs fabricated by low dose, high energy implantation of Ge (∼1×108, cm−2, 1.4 and 6.0 MeV) were used to monitor injection of point defects formed by low energy implants or Pd silicides. It was found that evaporation of Pd on preimplanted Si leads to a significant reduction of both the di‐vacancy and O‐vacancy signals, indicating injection of Si interstitials during the silicide formation. On the other hand low energy implants (52 keV Ge, 1×1013−5×1014cm−2) resulted only in a small reduction of these signals probably due to self‐trapping of the created interstitials, and furthermore prevented the reduction from the silicide formation, due to trapping of the injected interstitials in the damaged layer. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116475

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A tuning technique for mutual phase locking of two vertically stacked long Josephson junctions is suggested and successfully tested. The technique is based on passing a current through the middle electrode between two tunnel barriers. Mutually synchronized oscillation modes in the Nb/Al–AlOx/Nb stack are found to be tunable in the frequency range from 180 to 420 GHz. Presented results extend the possibility of using stacked long Josephson junctions as coherently operating oscillators for millimeter and submillimeter wave bands. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115652

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have deposited Bi2Sr2CaCu2O8+&dgr;/Bi2Sr2YCu2O8+&dgr;/Bi2Sr2CaCu2O+&dgr;(2212/22Y2/2212) heterostructures by aninsitudc sputtering technique at high oxygen pressures on (001) SrTiO3substrates. The formation of highlyc‐axis oriented trilayers with sharp interfaces is demonstrated by x‐ray diffraction and transmission electron microscope (TEM) analysis. Both the top and the bottom 2212 layers are superconducting below 87 K. Tunneling phenomena on junctions fabricated from these trilayers are observed. The conductance versus voltage curves at low temperatures exhibit a change of slope indicative of a gap structure at about 30 mV, a zero‐bias peak, as well as linear background at high voltages. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115653

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have studied the magnetization of amorphous Co–Dy–B and Fe–Dy–B alloys at 1.5 K under very high fields up to 35 T. Above a critical field the antiferromagnetic coupling breaks as indicated by the strong increase in the magnetization. This is explained by a model. The analysis of this behavior enables us to obtain some important parameters of fundamental interest, such as, the molecular field coefficient, the exchange integral, etc. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115654

出版商:AIP    

年代:1996

数据来源: AIP